Luminance adjusting circuit

Abstract

A luminance adjusting circuit includes an LED module, a switch module and a processing unit. A table equating luminance levels and average current values is pre-stored. The processing unit includes a judging and executing module and a signal generating module. The judging and executing module achieves a desired luminance level according to trigger signals generated by a button. The signal generating module produces timing signals to turn on and turn off the switch module periodically, thereby achieving an average current value to adjust the luminance level of the LED module to the desired level.

What is claimed is: 
     
       1. A luminance adjusting circuit, comprising:
 an integrated circuit configured for converting alternating current provided by a power supply into direct current; 
 an LED (light emitting diode) module comprising a plurality of LEDs; 
 a button module configured for creating trigger signals in response to user's operation on the button module; 
 a switch module connected to the LED module; 
 a processing unit comprising:
 a storage module configured for storing a table defining a relationship between luminance levels of the LED module and average current flowing through the LED module; 
 a judging and executing module configured for determine a desired luminance level according to the trigger signals, and further determines the average value of the current in the table corresponding to the desired luminance level; and 
 a signal generating module connected to the switch module, and configured for producing a timing signal according to the average value of the current required controlled by the judging and executing module, to turn on or off the switch module periodically for adjusting a current flowing through the LED module to obtain an average current value which according to the table equates to the desired luminance level, thereby adjusting the luminance level of the LED module to the desired the luminance level. 
 
 
     
     
       2. The luminance adjusting circuit as recited in  claim 1 , wherein the judging and executing module determines the luminance level of the LED module from a lower level to a higher level circularly according to the number of the trigger signals. 
     
     
       3. The luminance adjusting circuit as recited in  claim 1 , wherein the time signal defines a first control signal and a first endurance time of the first control signal, and a second control signal and a second endurance time of the second control signal periodically. 
     
     
       4. The luminance adjusting circuit as recited in  claim 3 , wherein the switch module is turned on in response to the first control signal, and turned off in response to the second control signal. 
     
     
       5. The luminance adjusting circuit as recited in  claim 3 , wherein the first control signal is a high level signal, and the second control signal is a low level signal. 
     
     
       6. The luminance adjusting circuit as recited in  claim 1 , wherein the integrated circuit comprises a bridge rectifier, and configured for converting an alternating current with full-wave in each period provided by the power supply into a direct current with two half-wave in each period which flows to the LED module. 
     
     
       7. The luminance adjusting circuit as recited in  claim 1 , further comprising:
 a current detecting unit connected between the switch module and the processing unit, and configured for detecting the currents flowing through the LED module; 
 the processing unit further comprising: 
 a calculating module connected to the current detecting unit, and configured for calculating an average value of the current in a predetermined period according to the currents detected by the current detecting unit; 
 wherein the judging and executing module further is configured for comparing the average value of the current calculated by the calculating module with the average value of the current defined in the table corresponding to the luminance level of the LED module, and controls the signal generating module to produce the timing signal correspondingly to monitoring and adjusts the luminance level of the LED module. 
 
     
     
       8. The luminance adjusting circuit as recited in  claim 1 , further comprising a voltage detecting unit connected between the integrated circuit and the judging and executing module, wherein the voltage detecting unit is configured for detecting the output voltage of the integrated circuit. 
     
     
       9. The luminance adjusting circuit as recited in  claim 8 , wherein the judging and executing module is further configured for determining whether the output voltage is lower than a preset voltage or not, and controls the signal generating module to produce a signal to turn off the switch module correspondingly when the output voltage is determined to be lower than the preset voltage. 
     
     
       10. The luminance adjusting circuit as recited in  claim 9 , wherein the preset voltage is a minimum working voltage of the LED module. 
     
     
       11. The luminance adjusting circuit as recited in  claim 1 , the switch module comprises a control terminal connected to the signal generating module, a first conduction terminal connected to the current detecting unit, and a second conduction terminal connected to the LED module.